Combustion apparatus of gas turbine engines with means controlling air flow conditions in the combustion apparatus



Feb. 6 1962 F. R. MURRAY 3,019,605

COMBUSTION APPARATUS OF GAS TURBINE ENGI WITH MEAN ONTROLLING AIR FLOW CONDITI S THE COMBUSTION APPARATUS Filed Nov. 18, 1957 5 Sheets-Sheet 1 Feb. 6, 1962 F. R. MURRAY 3,019,605

COMBUSTION APPARATUS OF GAS TURBINE ENGINES WITH MEANS CONTROLLING AIR FLOW CONDITIONS IN THE COMBUSTION APPARATUS Filed Nov. 18, 1957 5 Sheets-Sheet 2 Feb. 6, 1962 MURRAY 3,019,605

COMBUSTION APPARATUS OF GAS TURBINE ENGINES WITH MEANS CONTROLLING AIR FLOW CONDITIONS IN THE COMBUSTION APPARATUS Filed Nov. 18, 1957 5 Sheets-Sheet 3 Feb. 6, 1962 R, MURRAY 3,019,605

COMBUSTION APPARATUS OF GAS TURBINE ENGINES WITH MEANS CONTROLLING AIR FLOW CONDITIONS IN THE COMBUSTION APPARATUS Filed Nov. 18, 1957 5 Sheets-Sheet 4 Feb. 6, 1962 F. R. MURRAY 3,019,605 COMBUSTION APPARATUS OF GAS TURBINE ENGINES WITH MEANS CONTROLLING AIR FLOW CONDITIONS COMBUSTIUN APPARATUS F GAS TURBINE ENGINES WITH MEANS CGNT'RGLLING AIR FLOW CUNDITIONS IN THE COMBUSTION AP- PARATUS Frederick Reginald Murray, Newstead Abbey, Linby,

England, assignor to Roils-Royce Limited, Derby, England, a British company Filed Nev. 18, 1957, Ser. No. $7,068 Claims priority, application Great Britain Nov. 21, 1956 15 Ciaims. (Cl. 6039.65)

This invention comprises improvements in or relating to combustion equipment of gas-turbine engines and is concerned with combustion equipment of the kind (hereinafter referred to as the kind specified) comprising an air casing and, within the air casing, 21 flame tube wherein combustion occurs, the flame tube walls being spaced from the air casing to allow air to flow around the outside of the flame tube and having them circumferentially-spaced apertures through which the air flows into the flame tube. The air flowing through the apertures is usually termed secondary air and dilution or tertiary air, the secondary air being introduced into the flame tube to complete combustion and the dilution air being introduced to mix with the combustion products to cool them before they pass to the turbine.

In one form of combustion equipment of the kind specified, there are a number of tubular air casings each with an individual flame tube. In another form of such combustion equipment, there is a single annular air casing having radially-spaced coaxial walls and a plurality of flame tubes disposed in the annular space between the air casing walls. In yet another form of such combustion equipment, there is a single annular air casing having radially-spaced coaxial walls and a flame tube of annular form disposed within the space between the walls to be coaxial with them.

It has now been observed that, with combustion equipment of the kind specified, an irregular temperature distribution occurs at the outlet of the combustion equipment and it has now been found that one of the causes is the irregular formation of vortices in the secondary and tertiary air flowing in the air space and through the apertures into the flame tube and to cross flows in the air space downstream of the apertures. This effect is most marked in the third form of combustion equipment above described but also occurs in the other form of combustion equipment especially when the pressure drop between the air space and the interior of the flame tube is low.

This invention has for an object to' provide a construction of combustion equipment of the kind specified in which the irregular formation of vortices is reduced.

According to the present invention, combustion equipment of the kind specified comprises, in the region of the apertures, flow dividing walls each of which is in the air space between the air casing and flame tube, extends within the air space radially of the flame tube wall and axially of the combustion equipment across an aperture to divide the air flow to the aperture. By dividing the flow to the apertures in this way, a more regular vortex formation and a better temperature distribution is achieved.

According to a preferred feature of the invention, there is also provided an annular radially extending wall encircling the flame tube and joining the downstream ends of the flow-dividing walls. By providing such an annular Wall a marked improvement is achieved as compared with constructions in Which the annular wall is omitted. In one construction, the annular wall is contained in a plane at right angles to the flame tube axis, and in another construction, the wall is of zig-zag form arranged to 3 bi 5% 2 2 9 Fatenteci Feb. 6, 1962 shroud the downstream end of each aperture from the adjacent apertures. In another arrangement, the annular wall is provided by the flame tube itself at its junction with the air casing and in this case the radial walls will be extended downstream to this point. In yet another arrangement, the annular wall is frusto-conical with its upstream end adjacent the air casing and its downstream end adjacent the flame'tube.

Preferably, also, the radial and annular walls extend outwards to the air casing wall. When a clearance is left between these walls and the air casing wall, the clearance should preferably be small for example 12% of the radial spacing of the flame tube and air casing when the combustion equipment is in operation.

The upstream portion of the radial walls may be tapered to increase in depth from their upstream edges.

Some constructions of combustion equipment of this invention will now be described with reference to the accompanying drawings, in which FIGURE 1 is a developed view of one construction,

FIGURE 2 is a section on the line 22 of FIGURE 1,

FIGURE 3 is a view corresponding to FIGURE 1 of a second construction,

FIGURE 4 is a view corresponding to FIGURE 1 of a third construction,

FIGURE 5 is a view corresponding to FIGURE 2 of a modified form of FIGURE 4,

FIGURE 6 is a view corresponding to FIGURE 5 of a modification of the ararngement of FIGURE 5,

FIGURE 7 is an axial section through fully-annular combustion equipment of a gas-turbine engine and shows another form of the invention,

FIGURE 8 is a view corresponding to FIGURE 7 showing a modification,

FIGURE 9 is an axial section through combustion equipment of the kind having an annular air casing and a series of flame tubes in the air casing and shows another form of the invention, FIGURE 10 is a'section on the line 10-10 of FIG- URE 9, and shows the section line 9-9 of FIGURE 9, and

FIGURES 11 and 12 are sections on the lines 11-11 and 1212 respectively of FIGURE 10.

Referring to FIGURES 1 and 2, the combustion equipment comprises an air casing 10 and a flame tube 11 in the wall of which a ring of circumferentially-spaced apen tures 12 are provided for the flow of secondary and tertiary air from the air space 13 afiorded between the flame tube and air casing into the mixing zone 14 for the combustion products and dilution air. The apertures 12 may have any convenient shape.

In order to prevent or reduce the irregular formation of vortices in the air flowing through the space 13 and through the apertures 12, each aperture has associated with it a flow-dividing wall 15 which extends radially from the flame tube outwards across space 13 to the air casing and which extends axially from just upstream of the aperture along its centr line to just downstream of it. In this way, the flow of air in each aperture is divided and the irregular formation of large vortices in the air flowing through the apertures is avoided.

Referring now to FIGURE 3, in addition to the flowdividing walls 15 there is provided an annular wall 16 which joins the downstream ends of the walls 15. The wall 16 may have a radial extent similar to either of the forms of the wall 17 shown in FIGURE 5 and in FIG- URE 6. The wall 16 is contained in a plane at right angles to the flame tube axis and extends outwards from the flame tube to the air casing 10, With this arrangement not only is the irregular formation of large vortices avoid, but also extensive cross-flows of air downstream of the apertures 12 are avoided.

Referring to FIGURE 4, instead of the plain annular wall 16, there is provided an annular'wall '17 which is of zig-zag form, to join the downstream ends of the flowdividing walls 15. It will be seen that portions of the wall 17 extend upstream from the downstream ends of the walls 15 to penetrate the spaces between the apertures 12 and to shroud the downstream end of each aperture 12 from the adjacent apertures. Such arrangement has an eflect similar to the construction of FIGURE 3, but also markedly reduces local cross-flow between the apentures 12.

If desired, instead of flow-dividingwall 15 of uniform radial dimension, flow-dividing walls 13 may be provided, for example 'as shown in FIGURE for a construction of combustion equipment'similar to FIGURE 4, which taper from adjacent their mid-axial dimension to their upstream edges.

The flow-dividing walls 15, 18 may but e a clearance 19 from theair casing for'example as shown in FIGURE 6, but such clearance should preferably be small, for example about 12% of the radial spacing r the flame tube 11' and theair casing 10, so that extensive cross-flows do not occur radially beyond the walls 15,18. x

Rfer ringnow to FIGURE 7 the combustion equipment illustrated is of the fully-annular kind, that is it comprises an air casing having coaxial radially-spaced inner and outer walls 20, 21 respectively and within'the space between the walls 20, 21 an annular flame tube structure coaxial with the air casing and comprising radially-spacing inner and outer walls 22, 23 respectively defining the combustion -space 24 between them.

In use, air enters the combustionequipment from a compressor through an inlet 25. Partof the air (the primary air) flows directly into the flame tube through an inlet 26 and is further subdivided to flow partly through a space 27 housing fuel injection means (not shown) into the combustion space 24 and partly'into'passages 28 to enter the combustion space through apertures 29, The remainder, of the air (secondary and tertiary or dilution air) flows into annular passages 30 formed between the air casing walls 20, 21 andthe flame tube walls 22, 23 and this air enters the combustion 'space'throu'gh axiallyspaced sets of apertures 31, 32.

In order to promote a more regular formation of vortices in the air flowing through apertures 32 and to avoid undesirable cross-flows'in the passages 30 between the apertures 32, thereby to improve the temperature distribution at the outlet. 33 of the combustion equipment, there is provided a flow-dividing wall 34 in association with each aperture 32 and annular walls 35 joining the downstream ends of the walls 34.

In FIGURE 7, the flow-dividing walls 34 associated with the apertures 32 in the inner flame tube wall 22 are mounted on the inner air'casing wall by means of flanges 34a welded to the wall 20, and the Walls 34 extend axially from just upstream of the aperture 32 to adjacent the downstream ends of the apertures where they have tabs 34b welded to the annular wall 35. The wall 35 is frusto-conical and has a flange 35a by which the wall is welded to the air casing wall 20.

The flow-dividing walls 34 associated with the apertures 32 in the outer flame tube wall 23 are of similar construction having flanges 34a welded to the outer air casing wall 21 and tabs 34b'welded to the associated annular wall 35 which is frusto conical and is secured to the wall 21 by flange 35a. In FIGURE 8, the same references are used as in FIG- URE 7 to indicate like parts. In this constructiomthe flow-dividing walls 34 and annular Wall 35 associated with the' apertures 32 in the outer flame tube wall 23 are of the same construction as shown in FIGURE 7.

It will be seen that in FIGURES 7 and 8 the edges of the walls 34 are slightly radially spaced from the flame tube walls 22, 23. p

The flow-dividing Walls 134 associated with the apertures 32 in the inner flame tube wall 22 are in this construction secured to the flame tube wall '22. 'Eachwall 134 is welded at its upstream end 134a to the flame tube and has a rearward extension 134b formed with a tab 134a welded to a portion of the flame tube downstream of the apertures 32. The associated annular wall is again frusto-conical, but in this case is slightly spaced from the downstream ends of the walls 134. The annular wall 135 is attached to the air casing wall 20 over flange 13511. The inner edges of walls 134 are slightly radially spaced from the air casing wall 20. V

In FIGURES 9 to 12, there is shown a construction of combustion equipment for gas turbines in which there is an annular air casing having an inner wall 40 and a coaxial outer wall 41 and a series of flame tubes 42 disposed side by side in the annular space between the walls 40, 41 so that air passages 43 are formed outside the flame tubes 42 through which tertiary or dilution air flows to apertures 44 in the flame tubes 42.

Asis usual the flame tubes 42'have a downstream section 45 "provided at its upstream end with a narrow radially-outwardly extending flange 45a to which are welded-plates 46 which (as will be seen from FIGURE l0),"when the flametubes 42 are assembled, form a balfle substantially blocking the downstream ends of passages 43 just'downstream of the apertures 44. I I

In order to promote a more regular vortex formation in the air flowing through the apertures 44, each aperhim has associated with it a flowadividing wall 47a, 47b, 470 which are attached to the flame tube structure 42, 45, .46, extend axially from just upstream of the aperture 44 to downstream of it, and extend radially outwards from the flame tube to an extent dependent on the position of the aperture 44 around the flame tube.

The flow-dividing walls 47a have a small radial extent since the spacing of the flame tube and air casing wall 41 is small and these walls 47a are welded to flame tube at 48 and intoa slot'in the flange 45a.

The flow-dividing wall 47b associated with the apertures 44 which face adjacent flame tubes have an extent radially of the flame tube so that their outer edges. are close to the corresponding edges of the walls 47b on adjacent flame tubes. The walls 47b are welded at 49 (FIG- URE 12) to the flame tube and at their downstream ends have tabs 50 of substantial circumferential extent spot welded to the plates 46 or flange 45a.

The remaining flow-dividing walls 470 have'a large radial extent due to the large spacing of the associated apertures 44 from the air casing walls 40, 41. The walls 470 are welded to the flame tube 42 at 51 (FIGURE 11) and at their downstream ends have tabs 52 of substantial circumferential extent which are spot welded to the plates 46. v

The position of the spot welds securing tabs 50, 52 to the flame tube structure is selected to form flexible mountings for the walls 47b, 47c allowing for thermal expansion.

It will be seen that the walls 47a, 47b, 470 also project within the apertures 44 which have flanged peripheries.

I claim:

1. Combustion equipment of a gas-turbine engine com prising air casing structure and a flame tube defining a combustion space accommodated within the air casing structure, the flame tube having an air inlet at one end and an outlet at its opposite end, and said flame tube having a wall spaced away from the air casing structure to form an air space extending around the flame tube from adjacent the air inlet to adjacent'said outlet, there being circumferentially-spaced apertures in the flame tube wall adjacent said outlet establishing unobstructed communication between the air space and the combustion space for permitting a substantial flow of air from said air space into saidcombustion space, said apertures beginning and ending adjacent said outlet, and further comprising flowdividing walls disposed within the air space at said apertures, each flow-dividing wall extendingradially"across the air space from adjacent the flame tube wallto adjacent the air casing and extending axially of the flame tube across a corresponding one of the apertures to divide the air flowing from the air space towards the aperture, said flow-dividing walls being imperforate throughout their entire radial dimensions.

2. Combustion equipment according to claim 1, comprising also an annular radially extending wall encircling the flame tube and joining the downstream ends of the flow-dividing walls.

3. Combustion equipment according to claim 2, wherein the annular radially extending wall is contained in a plane at right angles to the flame tube axis.

4. Combustion equipment of a gas-turbine engine comprising air casing structure and a flame tube defining a combustion space accommodated within the air casing structure, the flame tube having an air inlet at one end and an outlet at its opposite end, and said flame tube having a wall spaced away from the air casing structure to form an air space extending around the flame tube from adjacent the air inlet to adjacent said outlet, there being circumferentially-spaced apertures in the flame tube wall at least adjacent said outlet permitting a substantial flow of air from said air space into said combustion space, and further comprising flow-dividing walls disposed within the air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing and extending axially of the flame tube across a corresponding one of the apertures to divide the air flowing from the air space towards the aperture, and an annular radially-extending wall of the zig-zag form encircling the flame, tube and joining the downstream ends of the flow-dividing walls, said annular zig-zag wall having portions extending upstream from the downstream ends of the flow-dividing walls between the apertures thereby to shroud the downstream end of each aperture from the adjacent aperture.

5. Combustion equipment according to claim 2, wherein the annular wall comprises a portion of the flame tube downstream of said circumferentially-spaced apertures, said portion of the flame tube extending to have a junction with the air casing structure, the radial flow dividing walls extending axially downstream to said portion of the flame tube.

6. Combustion equipment according to claim 2, wherein the annular wall is frusto-conical and has a larger diameter upstream end adjacent the air casing structure and a smaller diameter downstream end adjacent the flame tube.

7. Combustion equipment of a gas-turbine engine comprising air casing structure and a flame tube defining a combustion space accommodate within the air casing structure, the flame tube having an air inlet at one end and an outlet at its opposite end, and said flame tube having a wall spaced away from the air casing structure to form an air space extending around the flame tube from adjacent the air inlet to adjacent said outlet, there being circumferentially-spaced apertures in the flame tube wall at least adjacent said outlet permitting a substantial flow of air from said air space into said combustion space, and further comprising flow-dividing walls disposed within the air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing and extending axially of the flame tube across a corresponding one of the apertures to divide the air flowing from the air space towards the aperture, each said flow-dividing wall decreasing in radial dimension in a direction from its midaxial length to its upstream edge, and further comprising an annular radially-extending wall encircling the flame tube and joining the downstream edges of the flow-dividing walls.

8. Combustion equipment of a gas-turbine engine comprising air casing structure and a flame tube defining a 6 combustion space accommodated within the air casing structure, the flame tube having an air inlet at one end and an outlet at its opposite end, and said flame tube having a wall spaced away from the air casing structure to form an air space extending around the flame tube from adjacent the air inlet to adjacent said outlet, there being circumferentially-spaced apertures in the flame tube wall at least adjacent said outlet permitting a substantial flow of air from said air space into said combustion space, and further comprising flow-dividing walls disposed withing the air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing and extending axially of the flame tube across a corresponding one of the apertures to divide the air flowing from the air space towards the aperture, and an annular radially-extending wall encircling the flame tube and joining the downstream ends of the flow-dividing walls, said flow-dividing walls and the annular radially-extending wall having a small radial clearance from the air casing structure.

9. Combustion equipment according to claim 8, wherein said small radial clearance is substantially equal to 12% of the radial spacing of the flame tube wall and the air casing.

10. Combustion equipment of a gas-turbine engine comprising an air casing structure including radially-spaced coaxial inner and outer air casing walls, a flame tube structure disposed within the space between said air casing walls and comprising radially-spaced inner and outer flame tube walls coaxial with said air casing walls, said flame tube walls defining between them a combustion space having an inlet at one end and an outlet at the other end and said flame tube walls being radially spaced from the air casing Walls to form air spaces between the flame tube structure and the air casing structure, said air spaces extending axially from adjacent the said inlet to adjacent said outlet, there being circumferentially-spaced apertures in each of said flame tube walls at least adjacent said outlet permitting a substantial flow of air from said air spaces into said combustion space, and further comprising flow-dividing walls disposed within each air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing wall and extending axially of the flame tube structure across a corresponding one of said apertures to divide the air flowing from the air space towards the aperture, and comprising in each air space an annular radially-extending wall joining the downstream ends of the flow-dividing walls, the flow-dividing walls and annular wall associated with the apertures in the outer flame tube Wall being mounted on the outer air casing wall, and the flow-dividing walls and annular wall associated with the apertures in the inner flame tube wall eing mounted on the inner air casing walls, the edges of the flow-dividing walls and annular Walls being spaced from the associated flame tube wall.

11. Combustion equipment of a gas-turbine engine comprising an air casing structure including radiallyspaced coaxial inner and outer air casing walls, a flame tube structure disposed within the space between said air casing walls and comprising radially-spaced inner and outer flame tube walls coaxial with said air casing walls, said flame tube walls defining between them a combustion space having an inlet at one end and an outlet at the other end and said flame tube walls being radially spaced from the air casing walls to form air spaces between the flame tube structure and the air casing structure, said air spaces extending axially from adjacent the said inlet to adjacent said outlet, there being circumferentially spaced apertures in each of said flame tube walls at least adjacent said outlet permitting a substantial flow of air from said air spaces into said combustion space, and further comprising flow-dividing walls disposed within each air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing wall and extending axially of the flame tube structure across a corresponding one of said apertures to divide the air flowing from the air space towards the aperture, and comprising in each air space an annular radially-extending wall joining the downstream ends of the flow-dividing walls, the flow-dividing walls and annular wall associated with the apertures in the outer flame tube wall being mounted on the outer air casing wall and having their edges spaced from the outer flame tube wall, the flow-dividing walls associated with the apertures in the inner flame tube wall being mounted on it and having their edges spaced from the inner air casing wall, and the annular wall associated with the inner flame tube wall being mounted on the inner air casing wall, having its edge spaced from the inner flame tube wall and being slightly spaced downstream from the downstream ends of the flow-dividing walls.

12. Combustion equipment of a gas-turbine engine comprising an air casing structure including radially-spaced coaxial inner and outer air casing walls, a flame tube structure disposed within the space between said air casing walls and comprising radially-spaced inner and outer flame tube walls coaxial with said air casing walls,said flame tube walls defining between them a combustion space having an inlet at one end and an outlet at the other end and said flame tube walls being radially spaced from the air casing walls to form air spaces between the flame tube structure and the air casing structure, said air spaces extending axially from adjacent the said inlet to adjacent said outlet, there being circumferentially-spaced apertures in each of said flame tube walls at least adjacent said outlet permitting a substantial flow of air from said air spaces into said combustion space, and further comprising flowdividing walls disposed within each air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing wall and extending axially of the flame tube structure across a corresponding one of said apertures to divide the air flowing from the air space towards the aperture, and comprising in each air space an annular radially extending wall joining the downstream ends of the flowdividing walls, the annular Walls being frusto-conical, having their upstream ends adjacent the associated air casing wall and their downstream ends adjacent the associated flame tube wall.

13. Combustion equipment of a gas-turbine engine comprising an air casing structure having radially-spaced coaxial inner and outer walls, a series of flame tubes arranged side by side in the space between said inner and outer walls of the air casing, each said flame tube defining within it a combustion space; each said flame tube having an air inlet at one end and an outlet at its opposite end, and each said flame tube having a wall spaced away from the air casing structure to form an air space extending around the flame tube from adjacent the air inlet to adjatcent said outlet, there being circumferentially-spaced aperlures in the flame tube wall at least adjacent said outlet permitting a substantial flow of air from said air space into said combustion space, and each flame tube having associated with it flow-dividing walls disposed within the air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing and extending axially of the flame tube across a corresponding one of the apertures to divide the air flowing from the air space towards the aperture; said flame tubes being provided adjacent their downstream ends with radial portions together forming a baflie substantially blocking the air space between the flame tubes and air casing downstream of the apertures and wherein flow-dividing walls extend axially from the upstream ends of the apertures to the battle.

14. Combustion equipment according to claim 13, wherein the flow-dividing walls are secured at their upstream ends to the flame tubes and at the downstream ends have tabs secured to the baflle in a manner providing a flexible connection.

15. Combustion equipment of a gas-turbine engine comprising an air casing structure including radially-spaced coaxial inner and outer air casing walls, a flame tube structure disposed within the space between said air casing walls and comprising radially-spaced inner and outer flame tube walls coaxial with said air casing walls, said flame tube walls defining between them a combustion space having an inlet at one end and an outlet at the other end and said flame tube walls being radially spaced from the air casing walls to form air spaces between the flame tube structure and the air casing structure, said air spaces extending axially from adjacent the said inlet to adjacent said outlet, there being circumferentially-spaced apertures in each of said flame tube walls at least adjacent said outlet permitting a substantial flow of air from said air spaces into said combua-stion space, and further comprising flow-dividing walls disposed within each air space at said apertures, each flow-dividing wall extending radially across the air space from adjacent the flame tube wall to adjacent the air casing Wall and extending axially of the flame tube structure across a corresponding one of said apertures to divide the air flowing from the air space towards the aperture, and comprising in each air space an annular radially-extending wall joining the downstream ends of the flow-dividing walls.

References Cited in the file of this patent UNITED STATES PATENTS 2,488,911 Hepburn Nov. 22, 1949 2,513,325 Hundstad July 4, 1950 2,601,000 Nerad June 17, 1952 2,616,258 Mock Nov. 4, 1952 2,618,928 Nathan Nov. 25, 1952 2,651,912 Abbott Sept. 15, 1953 2,770,096 Fox Nov. 13, 1953 2,756,731 Wille July 31, 1956 2,828,609 Ogilvie Apr. 1, 1958 

